1. Field of the Invention
The present invention relates to fluid drain structure located at a position intermediate the ends of a bed of media through which the fluid is passed vertically in being processed by the media. More particularly, the invention relates to the configuration provided the drain structure which will enable it to survive vertical bed movement, to a cleaning circuit for the drain structure and to a transfer system for the media of the bed to and from the vessel.
2. Description of the Prior Art
Beds of granular media placed inside vessels for fluids to be passed through the media have been common in the art for sometime. Most of these beds of media are used as more or less simple filters to remove undesirable material from the fluid. However, there is a wide range of materials which must be separated from streams of industrial fluid and there are many different materials useful as bed media for this processing.
The art was initially concerned with the relatively simple function of distributing the fluid to be filtered over the horizontal surface of the bed of media and the drain of the filtered liquid from the opposite horizontal surface. The distribution and drain structure were essentially plates with spaced apertures or porous bodies. These perforated plates and porous bodies were usually placed to span their vessel containing the media and placed at the face of the media bed within the vessel.
In broadly describing the structure which retains, or supports, media beds, it is recognized that fluids processed can be directed horizontally, as well as vertically, through the beds. In this prior art, consider primarily the vertical orientation. It is in the vertical flow pattern that a recent revolution has occurred.
Up-flow of processed fluids through media beds turned the porous underdrain structure supporting the beds into a distribution system. At least one example of this system is disclosed in U.S. Pat. No. 2,723,761, dated Nov. 15, 1955 to Van Der Made, et al. The advantages of this up-flow pattern have been established by the practice in the art which follows this disclosed system.
The drain system of the Van Der Made, et al. disclosure was embodied in a porous structure embedded below the upper surface of the media bed. The forces of up-flow on the bed were balanced by the downward pressure of liquid in the freeboard space above the bed. During the backwash cycle, this downward pressure was relieved to permit the bed to be expanded into the freeboard space.
The forces placed upon the drain structure in the vertical upflow bed have not concerned the prior art. Now a new concept has appeared and has been reduced to practice, and the forces placed upon drain structure mounted intermediate the upper and lower faces of the bed of media have proved to be destructive and the source of a very severe problem.
The new concept is disclosed in U.S. patent application Ser. No. 615,670 filed Sept. 22, 1975 by Charles R. Ferrin. In the system disclosed, a multi-media bed of granular material is placed in a vertical orientation. Carefully selected, the media has been graded coarse-to-fine in both the up-flow direction and the down-flow direction. Thus the coarse-to-fine grading made possible by the up-flow pattern has been made available in both directions in the same bed and within the same vessel. The advantages apparent in processing fluid by flowing it into both ends of the same bed and draining the processed fluid from a location intermediate the upper and lower surfaces of the bed were confirmed in the first test of the actual reduction to practice. All subsequent test data has been consistent.
The reduction to practice exposed the mechanical problem of mounting a drain structure at the intermediate location between the two vertical bed faces. The drain system disclosed in the Ferrin patent application was reduced to practice in the first model. The openings in the walls of the vessel conducted processing fluid from the outer edge of the bed. However, it become evident that the processed fluid should be drained from points across the horizontal area of the bed. Additionally, a significant quantity of debris found its way into the drain system during backwash of the bed. Also, the bed media necessary to obtain the coarse-to-fine grading in both directions proved expensive. There is a handling and storage problem of this valuable media during service periods.